i868 i88i] GALLS 425 



remarks on Herbert Spencer. 1 . . . Our recent visit to Cam- Letter 756 

 bridge was a brilliant success to us all, and will ever be 

 remembered by me with much pleasure. 



To James Paget. Letter 757 



During the closing years of his life, Darwin began to experimentise 

 on the possibility of producing galls artificially. A letter to Sir J. D. 

 Hooker (Nov. 3rd, 1880) shows the interest which he felt in the 

 question : 



" I was delighted with Paget's essay 2 ; I hear that he has occasionally 

 attended to this subject from his youth. ... I am very glad he has 

 called attention to galls : this has always seemed to me a profoundly 

 interesting subject ; and if I had been younger would take it up." 



His interest in this subject was connected with his ever-present wish 

 to learn something of the causes of variation. He imagined to himself 

 wonderful galls caused to appear on the ovaries of plants, and by these 

 means he thought it possible that the seed might be influenced, and thus 

 new varieties arise. 3 He made a considerable number of experiments by 

 injecting various reagents into the tissues of leaves, and with some slight 

 indications of success. 4 



The following letter to the late Sir James Paget refers to the same 

 subject. 



Down, Nov. I4th, 1880. 



I am very much obliged for your essay, which has inter- 

 ested me greatly. What indomitable activity you have ! It 

 is a surprising thought that the diseases of plants should 

 illustrate human pathology. I have the German Encyclopedia^ 

 and a few weeks ago told my son Francis that the article on 



1 Prof. Balfour discussed Mr. Herbert Spencer's views on the genesis 

 of the nervous system, and expressed the opinion that his hypothesis 

 was not borne out by recent discoveries. "The discovery that nerves 

 have been developed from processes of epithelial cells gives a very 

 different conception of their genesis to that of Herbert Spencer, which 

 makes them originate from the passage of nervous impulses through a 

 track of mingled colloids. . . ." (loc. cit., p. 644.) 



2 An address on "Elemental Pathology," delivered before the British 

 Medical Association, August 1880, and published in the Journal of the 

 Association. 



3 There would have been great difficulties about this line of research, 

 for when the sexual organs of plants are deformed by parasites (in the 

 way he hoped to effect by poisons) sterility almost always results. See 

 Molliard's "Les Cecidies Florales," Ann. Set. Nat., 1895, Vol. I., p. 228. 



The above passage is reprinted, with alterations, from Life and 

 Letters^ III., p. 346. 



